Wednesday, July 7, 2010

Stripping Neon

The Linac Coherent Light Source (LCLS) delivers an intense pulse of X-rays designed to image atoms and molecules.
When the LCLS X-rays are tightly focused by mirrors, each pulse destroys any sample it hits.

LCLS pulses have been used to strip electrons away from atoms of neon one at a time.
Using a shorter pulse, fewer electrons are stripped away and less damage is done.
By varying the photon energies of the pulses, the electrons can be removed from the outside in, or, from the inside out creating so-called " hollow atoms".

The 2 electrons in the innermost electron shell closest to the nucleus are the hardest to strip away, but they also most readily absorb photons of X-ray light and so are the most vulnerable to being stripped away by intense X-rays. At low photon energies, the outer electrons are removed, leaving the inner electrons untouched. At higher photon energies the inner electrons are the first to be ejected, then the outer electrons cascade into the empty inner core, only to be kicked out by later parts of the same X-ray pulse.

Reference:
L. Young, E. P. Kanter, B. Krässig, Y. Li, A. M. March, S. T. Pratt, R. Santra, S. H. Southworth, N. Rohringer, L. F. DiMauro, G. Doumy, C. A. Roedig, N. Berrah, L. Fang, M. Hoener, P. H. Bucksbaum, J. P. Cryan, S. Ghimire, J. M. Glownia, D. A. Reis, J. D. Bozek, C. Bostedt, M. Messerschmidt. Femtosecond electronic response of atoms to ultra-intense X-rays. Nature, 2010; 466 (7302): 56 DOI: 10.1038/nature09177


Study Questions
  1. What is the name given to the removal of electrons from a gaseous atom?
  2. What is the charge resulting from the removal of an electron from a neon atom?
  3. Write the electron configuration for the neon atom and for the species produced after an electron has been removed.
  4. Write an equation to show the removal of an electron from a gaseous neon atom.
  5. In a similar set of experiments, nitrogen was used instead of neon. Write the electron configuration of a nitrogen atom and of the species produced after an electron has been removed.
  6. Do you think it would be easier to remove an electron from an atom of neon or from an atom of nitrogen? Explain your answer.
  7. Why do you think the researchers chose to use neon and nitrogen gases for these experiments?

No comments:

Post a Comment